1. Field of the Invention
The present invention relates to tools, such as automatic drills, and more particularly, to a method and apparatus for reversing a fluid driven motor of such tools.
2. Description of the Related Art
Fluid driven motors, such as air driven or liquid driven motors, are widely used in industry, particularly in portable tools. For example, radial vane air motors, or pneumatic motors, are used in portable air tools, such as nut runners and right angle positive feed drills. In many instances, it is desirable to reverse the motor of such tools. For instance, with some right angle positive feed drills, reversing the air motor causes a spindle and drill bit to rapidly advance toward a workpiece. Rapidly advancing the drill bit toward the workpiece saves considerable time because, without the rapid advance option, an operator of the tool must wait for the spindle to advance slowly toward the workpiece during a drilling cycle. Hence, many conventional tools include an air motor that is reversible.
Conventional reversible air motors typically include a bearing plate having an axially oriented inlet port and an axially oriented outlet port. Such air motors are run in a forward direction by directing air flow through the inlet port and by permitting exhaust air to exit the outlet port. To reverse such air motors, the air flow is shut off and the air porting is changed such that air will flow into the outlet port rather than the inlet port. In this case, the motor will turn in reverse and the inlet port will function as an exhaust port. This rerouting of the the air flow is typically achieved by an operator manually moving a switch or other similar device to directly move a ring located adjacent to the bearing plate having the inlet and outlet ports. After the operator has reversed the porting, the air supply is turned on to run the motor in reverse. Thus, two manual steps are required to reverse the air motor.
Other conventional tools use other approaches to reverse an air motor. For example, one such tool includes what is typically considered a non-reversible air motor. This air motor includes an axially oriented inlet port, but does not include an axially oriented outlet port as it is typically designed to rotate in one direction. Thus, the air motor includes a plurality of exhaust slots located along the periphery of air motor's housing. This air motor is run in a forward direction by directing air flow through the inlet passage and out of the above-described exhaust ports. To reverse this type of air motor, a shifting lever is actuated by an operator, which opens a ball valve. The opening of the ball valve permits pressurized air to flow into a deflector cavity. The pressurized air in the deflector cavity imposes a force against a pressure-actuated exhaust deflector that is slidably mounted on the outside of the motor housing. The exhaust deflector is moved and closes off the atmospheric exhaust route normally used during forward rotation of the motor. The incoming pressurized air in the deflector cavity is then routed to the normal exhaust slots of the motor such that the motor operates in reverse. Although this reversing method adequately reverses the motor of the tool, it requires many complicated parts in order for the reversing operation to function properly. For instance, the above-described construction requires kick-out springs in the motor to keep the blades thrown against the wall of the motor.
In yet another conventional approach to reversing an air motor of a tool, an operator actuates a button to cause a spool valve to reroute air flow to the inlet and outlet ports of a reversible air motor. However, this approach tends to reduce the power of the air motor, unless the spool valve is overly large. Additionally, this approach of reversing the air motor requires that the operator turn on the flow of pressurized air to the motor by actuating another device, such as an air valve.
Thus, it is apparent that conventional tools having a reversible air motor generally require two separate steps to reverse the motor--reversing the porting to the motor, and then supplying air to the motor to run it in reverse. These separate steps may create manufacturing problems and even damage the tool if the operator performs these steps in the wrong order or in combination with another sequence, such as a drilling cycle. Furthermore, conventional tools having an actuator that both reverses the porting to and from the air motor and supplies air to the motor are overly complicated. The above-described constraints and problems associated with conventional tools has created a need for a new approach to reverse an air motor.